An acknowledge channel is used on the reverse channel in a wireless communications system operating in accordance with CDMA2000 standards to signal the base station whether a data packet transmitted on the downlink channel has been received by the mobile terminal. The mobile terminal sends an ACK symbol (+1) when it has successfully recovered the downlink data packet, a NACK symbol (−1) when it has received the packet data but has not recovered it successfully, and a NULL symbol (0) when the mobile terminal doesn't receive anything and remains quiet and sends nothing.
A base station receiver in such a system thus needs to recover the symbol (ACK, NACK, or NULL) sent on the acknowledge channel in order to determine whether it needs to retransmit the data packet again. Such a receiver thus comprises a three-state detector that makes a decision whether an ACK, a NACK, or a NULL has been transmitted by the mobile terminal on the acknowledge channel. The performance of the three-state detector directly impacts the network throughput. Traditionally, a three-state detector is designed to minimize the average probability of detection errors. Such a detector treats the error of detecting an ACK when a NACK was actually sent the same as the error of detecting a NACK when an ACK was actually sent, and so on. FIG. 1 illustrates prior art processing of a received signal “r” acknowledge signal by a base station receiver. As can be noted, after the signal “r” of magnitude R is received (step 101), a determination is made whether R is greater than a threshold T1 (step 102). If it is, then the decision is made that ACK was the symbol that was sent (step 103). If R it isn't greater than threshold T1, then R is compared with another threshold T2 (step 104). If R is less than T2, then the decision is made that NACK was the symbol that was sent (step 105). If, however R is greater than T2, then the decision is made that NULL was the symbol that was sent (step 106).
Disadvantageously, this prior art method does not provide optimal network performance in terms of network throughput. A three-state detector that aims at optimizing the network throughput is therefore desirable.